MESOSCALE PRECIPITATION DISCUSSION 0349
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
316 PM EDT TUE JUN 20 2017

AREAS AFFECTED...SOUTHEAST LA...COASTAL MS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 201915Z - 210000Z

SUMMARY...NORTHERN CONVERGENCE BAND TO TS CINDY.

DISCUSSION...RECENT GOES-16 EXPERIMENTAL AND RADAR TRENDS DENOTE A
SLIGHT INCREASE IN ELONGATION TOWARD THE NORTHEAST OF TS
CINDY...WV ALSO DENOTES A SLIGHT NORTHEAST PUNCH OF 7H-5H DRY AIR
AS FAR EAST AS 88W. THIS ORIENTATION IS STRENGTHENING LOW LEVEL
WIND FIELD CONVERGENCE WHILE SLIGHTLY INCREASING INSTABILITY
ALOFT.  IN RESPONSE CONVECTION HAS BEEN GROWING ALONG THE
NORTHERLY CONVERGENCE BAND WITH EIR TOPS ECLIPSING -80C.  WV LOOP
ALSO SHOWS SOLID 130-150 DEGREES OF OUTFLOW JET TO THE NORTH WITH
MODEST ANTICYCLONIC SUPER-GEOSTROPHIC EFFECTS FURTHER AIDING
DIVERGENCE ALOFT FOR CONVECTIVE GROWTH. THE CONVERGENCE BAND
SHOULD ROTATE NORTHWARD THEN WESTWARD WITH THE SW FLANK PIVOTED
NEAR THE NORTHERN PORTION OF THE INNER CENTER  SOUTH OF TERREBOUNE
BAY.  AS THE BAND ROTATES THROUGH SE LA...OVER THE NEXT THREE TO
FOUR HOURS...STRONG UPSTREAM CONVERGENCE PERHAPS ENHANCED ALONG
COAST AS FRICTIONAL EFFECTS TO ALLOW FOR REGENERATION/BACKBUILDING
THROUGH THE EVENING HOURS ACROSS SE LA.   GIVEN TOTAL PWS OVER
2.5" AND CONVERGENT WINDS IN EXCESS OF 40KTS...FLUX WILL BE HIGH
WITH EXTREME RAINFALL EFFICIENCY WITH 3"/HR RAIN RATES
LIKELY...WITH STRIPES OF 3-5" ARE PROBABLE OVER SE LA...WITH 6"+
LOCALIZED TOTALS NOT OUT OF THE QUESTION.

FURTHER NORTHEAST INTO COASTAL MS...FASTER CELL MOTIONS FURTHER
FROM THE PIVOT AREA ARE EXPECTED AND SO RAINFALL TOTALS SHOULD BE
LESS...STILL STRONG ONSHORE FLOW AND CLOSER PROXIMITY FOR
INCREASED DIVERGENCE MAY ALLOW FOR EVEN DEEPER AND MORE EXPANSIVE
CONVECTIVE CORES...SPREADING THE WEALTH ACROSS THE COASTAL
COUNTIES WITH 2-3" POSSIBLE WITH ISOLATED TOTALS TO 4". 

STRONGER CONVERGENCE UPSTREAM AND NARROWING OF FOCUS OF THE
EASTERN BAND IS STILL IN SOME QUESTION ON TIMING NEARING THE COAST
AS WELL AS PLACEMENT LONGITUDINALLY...AND AS SUCH AN ADDITIONAL
MPD MAY BE NEEDED EARLIER THAN 00Z FOR MS/AL/W FL COAST. 

GALLINA

ATTN...WFO...LCH...LIX...

ATTN...RFC...LMRFC...

LAT...LON   30578935 30538873 30218851 29248887 28928918
            29038964 28998999 28869046 29049108 29419150
            29789126 30029081 30419024